Search

It is known that, in the proximity of a neutral wall, liquids experience diffusion enhancement relative to their bulk diffusion, but the origin of this phenomenon is still unknown. We report a molecular dynamics simulation investigating the dynamics of a simple liquid in the proximity to a non-interacting smooth confining wall, which exhibits a strong diffusion enhancement within the liquid layers adjacent to the wall. We present an analysis of these results, demonstrating that the observed diffusion enhancement can be accounted for, with numerical accuracy, using the universal scaling law that relates the liquid diffusion rate to the excess entropy. These results show that the scaling law, which has so far only been used for the description of the bulk liquid diffusion, can be successfully used to describe the diffusion in liquids under nano-scale confinement. [ABSTRACT FROM AUTHOR]

Since the 1940s, it has been known that diffusion in crystalline solids occurs due to lattice defects. The diffusion of defects can have a great impact on the processing and heat treatment of materials as the microstructural changes caused by diffusion can influence the material qualities and properties. It is, therefore, vital to be able to control the diffusion. This implies that we need a deep understanding of the interactions between impurities, matrix atoms, and intrinsic defects. The role of density functional theory (DFT) calculations in solid-state diffusion studies has become considerable. The main parameters to obtain in defect diffusion studies with DFT are formation energies, binding energies, and migration barriers. In particular, the utilization of the nudged elastic band and the dimer methods has improved the accuracy of these parameters. In systematic diffusion studies, the combination of experimentally obtained results and theoretical predictions can reveal information about the atomic diffusion processes. The combination of the theoretical predictions and the experimental results gives a unique opportunity to compare parameters found from the different methods and gain knowledge about atomic migration. In this Perspective paper, we present case studies on defect diffusion in wide bandgap semiconductors. The case studies cover examples from the three diffusion models: free diffusion, trap-limited diffusion, and reaction diffusion. We focus on the role of DFT in these studies combined with results obtained with the experimental techniques secondary ion mass spectrometry and deep-level transient spectroscopy combined with diffusion simulations. [ABSTRACT FROM AUTHOR]

1H spin-lattice Nuclear Magnetic Resonance relaxometry experiments have been performed for collagen and collagen-based artificial tissues in the frequency range of 10 kHz–20 MHz. The studies were performed for non-hydrated and hydrated materials. The relaxation data have been interpreted as including relaxation contributions originating from 1H–1H and 1H–14N dipole–dipole interactions, the latter leading to Quadrupole Relaxation Enhancement effects. The 1H–1H relaxation contributions have been decomposed into terms associated with dynamical processes on different time scales. A comparison of the parameters for the non-hydrated and hydrated systems has shown that hydration leads to a decrease in the dipolar relaxation constants without significantly affecting the dynamical processes. In the next step, the relaxation data for the hydrated systems were interpreted in terms of a model assuming two-dimensional translational diffusion of water molecules in the vicinity of the macromolecular surfaces and a sub-diffusive motion leading to a power law of the frequency dependencies of the relaxation rates. It was found that the water diffusion process is slowed down by at least two orders of magnitude compared to bulk water diffusion. The frequency dependencies of the relaxation rates in hydrated tissues and hydrated collagen are characterized by different power laws ( ω H − β , where ωH denotes the 1H resonance frequency): the first of about 0.4 and the second close to unity. [ABSTRACT FROM AUTHOR]

Graphene-based applications, such as supercapacitors or capacitive deionization, take place in an aqueous environment, and they benefit from molecular-level insights into the behavior of aqueous electrolyte solutions in single-digit graphene nanopores with a size comparable to a few molecular diameters. Under single-digit graphene nanoconfinement (smallest dimension <2 nm), water and ions behave drastically different than in the bulk. Most aqueous electrolytes in the graphene-based applications as well as in nature contain a mix of electrolytes. We study several prototypical aqueous mixed alkali-chloride electrolytes containing an equimolar fraction of Li/Na, Li/K, or Na/K cations confined between neutral and positively or negatively charged parallel graphene sheets. The strong hydration shell of small Li+ vs a larger Na+ or large K+ with weaker or weak hydration shells affects the interplay between the ions's propensity to hydrate or dehydrate under the graphene nanoconfinement and the strength of the ion–graphene interactions mediated by confinement-induced layered water. We perform molecular dynamics simulations of the confined mixed-cation electrolytes using the effectively polarizable force field for electrolyte–graphene systems and focused on a relation between the electrochemical adsorption and structural properties of the water molecules and ions and their diffusion behavior. The simulations show that the one-layer nanoslits have the biggest impact on the ions' adsorption and the water and ions' diffusion. The positively charged one-layer nanoslits only allow for Cl− adsorption and strengthen the intermolecular bonding, which along with the ultrathin confinement substantially reduces the water and Cl− diffusion. In contrast, the negatively charged one-layer nanoslits only allow for adsorption of weakly hydrated Na+ or K+ and substantially break up the non-covalent bond network, which leads to the enhancement of the water and Na+ or K+ diffusion up to or even above the bulk diffusion. In wider nanoslits, cations adsorb closer to the graphene surfaces than Cl−'s with preferential adsorption of a weakly hydrated cation over a strongly hydrated cation. The positive graphene charge has an intuitive effect on the adsorption of weakly hydrated Na+'s or K+'s and Cl−'s and a counterintuitive effect on the adsorption of strongly hydrated Li+'s. On the other hand, the negative surface charge has an intuitive effect on the adsorption of both types of cations and only mild intuitive or counterintuitive effects on the Cl− adsorption. The diffusion of water molecules and ions confined in the wider nanoslits is reduced with respect to the bulk diffusion, more for the positive graphene charge, which strengthened the intermolecular bonding, and less for the negative surface charge, which weakened the non-covalent bond network. [ABSTRACT FROM AUTHOR]

We study alchemical atomic energy partitioning as a method to estimate atomization energies from atomic contributions, which are defined in physically rigorous and general ways through the use of the uniform electron gas as a joint reference. We analyze quantitatively the relation between atomic energies and their local environment using a dataset of 1325 organic molecules. The atomic energies are transferable across various molecules, enabling the prediction of atomization energies with a mean absolute error of 23 kcal/mol, comparable to simple statistical estimates but potentially more robust given their grounding in the physics-based decomposition scheme. A comparative analysis with other decomposition methods highlights its sensitivity to electrostatic variations, underlining its potential as a representation of the environment as well as in studying processes like diffusion in solids characterized by significant electrostatic shifts. [ABSTRACT FROM AUTHOR]

Scanning x-ray microbeam topography and fluorescence experiments were conducted in situ to study the electromigration behavior of a 0.5 μm thick, 10 μm wide, and 200 μm long Al(0.25 at. % Cu) conductor line with 1.5 μm-thick SiO2 passivation on a single crystal Si substrate. The strain sensitivity of x-ray topography measurement allowed detailed examination of the electromigration-induced stress distribution and evolution in the conductor line in response to the depletion of Cu solute early in the electromigration process. Upon electromigration at 0.4 MA/cm2 and 303 °C, a short-range stress gradient was quickly induced by Al migration in the Cu-depleted cathode region to counteract further Al flow. The stress gradient was fully developed during the 5.3 h incubation time, extending over the critical Blech length of about 66 μm from the cathode end. Plastic deformation then occurred at the downstream end of the Cu-depleted region. The preferential electromigration of Cu did not cause detectable stress change outside the Cu-depleted region, except for the significant stress development from the Al2Cu precipitation at the anode end which appeared to initiate the fracture in the passivation. Preliminary finite difference modeling was undertaken to simulate the experimental observations, from which important parameters dictating electromigration in Al(Cu) line were extracted: an apparent effective valence of −5.6 and −1.9 for Cu and Al in Al(Cu), respectively, and a critical Cu concentration of 0.16 at. % above which Al grain boundary diffusion is effectively blocked. [ABSTRACT FROM AUTHOR]

Transition state calculation is a critical technique to understand and predict versatile dynamical phenomena in solids. However, the transition state results obtained at 0 K are often utilized for the prediction or interpretation of dynamical processes at high temperatures, and the error bars of such an approximation are largely unknown. In this benchmark study, all the major temperature effects, including lattice expansion, lattice vibration, electron excitation, and band-edge shift, are evaluated with first-principles calculations for defect diffusion in solids. With the inclusion of these temperature effects, the notable discrepancies between theoretical predictions at 0 K and the experimental diffusivities at high temperatures are dramatically reduced. In particular, we find that lattice expansion and lattice vibration are the dominant factors lowering the defect formation energies and hopping barriers at high temperatures, but the electron excitation exhibits minor effects. In sharp contrast to typical assumptions, the attempt frequency with lattice expansion and vibration varies significantly with materials: several THz for aluminum bulk but surprisingly over 500 THz for 4H-SiC. For defects in semiconductors, the band-edge shift is also significant at high temperatures and plays a vital role in defect diffusion. We expect that this study would help accurately predict the dynamical processes at high temperatures. [ABSTRACT FROM AUTHOR]

Germanium has received increased research interest for use in next-generation CMOS technology as its high carrier mobilities allow for enhanced device performance without further device scaling. Fabrication of high-performance NMOS Ge devices is hindered by high diffusivity and low activation of n-type implanted dopants. While the high solid solubility of P in Ge makes it an ideal dopant, its diffusion mechanism is poorly understood and results in heavy tradeoffs between implanted dopant diffusion and electrical activation. In this study, we demonstrate the suppression of in-diffusion of implanted P via a co-implantation with Ar. Diffusivity of implanted P species and their activation is investigated over a wide range of annealing temperatures and times. P diffusion was explored by secondary-ion-mass-spectrometry and the diffusivity of P was extracted by solving the 2D diffusion equation using the Crank–Nicolson method, and the dopant electrical activation was extracted from the Hall effect measurements. The co-implantation of P with Ar entirely suppresses P in-diffusion up to annealing temperatures as high as 700 °C but at the cost of its reduced electrical activation. Extracted diffusivity reveals a highly correlated exponential relationship with annealing. P activation energy was extracted from Arrhenius behavior. A 450 °C/10 min annealing of P implant shows negligible in-diffusion of P with the activation as high as 70%. RTA processing of the Ar/P co-implanted sample at 750 °C for 1 min results in a negligible P in-diffusion and an electrical activation of 20%. [ABSTRACT FROM AUTHOR]

Recently, nanostructuration has been proposed to improve the performance of phase change memories. This is the case of superlattices composed of amorphous carbon and crystalline germanium telluride, which we have investigated by molecular dynamics. For this, a modified Stillinger–Weber potential is adapted to reproduce their stiffness contrast/impedance ratio. In order to study the effect of the interface interaction, two sets of parameters are used to model the interfaces with different interactions between the two materials using the properties of the softer material or the average properties between the two creating an adaptation of impedance across the layers. The effects of interface roughness and carbon diffusion at grain boundaries are studied. Using equilibrium molecular dynamics as well as the propagation of wave-packets, we show first that without impedance adaptation, the anisotropy is high, and the roughness has a marked impact on the properties. However, the introduction of impedance adaptation destroys those effects on the thermal conductivity. Finally, we show that the periodic texturing of the interface increases the transmission of in-plane transverse phonons. [ABSTRACT FROM AUTHOR]

This work investigates the hydrogen embrittlement (HE) behavior of Nickel-201 alloy using experimental and numerical approaches. In experimentation, the effect of electrochemical hydrogen charging on the deformation behavior of tensile oligocrystals is investigated at different strain rates. Irrespective of the strain rate levels, all the hydrogen-charged tensile oligocrystals exhibited intergranular (IG) fracture exclusively along the random high-angle grain boundaries (RHAGBs). At the same time, no crack was observed along the coincident site lattice (CSL) Σ 3 type grain boundaries. The absence of an interconnected grain boundary network, lower stress levels, and insensitivity of H-induced IG fracture to the strain rate levels of investigated FCC oligocrystals (with low lattice hydrogen diffusion coefficient) established the insignificance of dynamic H-redistribution toward HE. In numerical simulations, a crystal plasticity-phase field fracture finite element model simulates the macroscopic tensile response and corresponding microscopic fracture evolution behavior for hydrogen-free and hydrogen-charged tensile oligocrystals. The experimental results corroborated by numerical simulations, validate that the reduction in fracture energy of RHAGBs, induced by hydrogen segregation through thermodynamic equilibrium during hydrogen charging prior to deformation, is the dominating factor governing HE. • Hydrogen embrittlement (HE) of Ni- oligocrystals at various strain rate is investigated. • Experimental results are corroborated by crystal plasticity-phase field fracture simulations. • H-induced intergranular fracture initiated and propagated along the RHAGBs only. • H-segregation by thermodynamic equilibrium established prior to deformation governs the HE. [ABSTRACT FROM AUTHOR]

The development of a high-power and long-life thermionic ceramic cathode poses significant challenges, namely the need for high electron emission capacity at low temperature and excellent machinability. In this paper, the first-principles method was used to obtain the (La 0.5 Ba 0.5)B 6 with the lowest work function, and (La 0.5 Ba 0.5)B 6 –ZrB 2 composite with high relative density of 98.08 % was prepared by spark plasma sintering (SPS) at T = 1800 °C, under which the densification mechanism transformed from the particle rearrangement into the grain boundary diffusion, and the corresponding apparent activation energies were 282.75 kJ/mol and 466.54 kJ/mol, respectively. The maximum current density of 12.93 A/cm2 at T = 1500 °C of the composite was higher than that of 11.71A/cm2 at T = 1600 °C of LaB 6 , which can be attributed to the high Fermi level and weak electronic constraints of (La 0.5 Ba 0.5)B 6. The practical work function distribution (PWFD) of 0.36 eV indicated the composite had excellent emission uniformity. [ABSTRACT FROM AUTHOR]

In situ age and trace element determinations of monazite, rutile and zircon grains from an ultrahigh temperature (UHT) metapelite‐hosted leucosome from the Napier Complex using laser split‐stream analysis reveal highly variable behaviour in both the U–Pb and trace element systematics that can be directly linked to the microstructural setting of individual grains. Monazite grains armoured by garnet and quartz retain two concordant ages 2.48 and 2.43 Ga that are consistent with the previously determined ages for peak UHT metamorphism in the Napier Complex. Yttrium in the armoured grains is unzoned with contents of ~700 ppm for the garnet‐hosted monazite and in the range 400–1,600 ppm for the monazite enclosed within quartz. A monazite grain hosted within mesoperthite records a spread of ages from 2.43 to 2.20 Ga and Y contents ranging between 400 and 1,700 ppm. This grain exhibits core to rim zoning in both Y and age, with the cores enriched in Y relative to the rim and younger ages in the core relative to the rim. A monazite grain that sits on a grain boundary between mesoperthite and garnet records the largest spread in ages—from 2.42 to 2.05 Ga. The youngest ages in this grain are within a linear feature that reaches the core and is connected to the grain boundary between the garnet and mesoperthite; the oldest ages are observed where monazite is in contact with garnet. Yttrium in the grain is enriched in the core and depleted at the rim with the strongest depletions where monazite is adjacent to grain boundaries between the silicate minerals or in contact with garnet. The unarmoured monazite grains have lower intercept ages of 1.85 Ga, which overlaps with the bulk of ages determined from the rutile and is coincident with a previously reported zircon age obtained through depth profiling from the Napier Complex. The age and chemical relationships outlined above illustrate decoupling between the geochemical and geochronological systems in monazite. Individual grains are suggestive of a range of processes that modify these systems, including volume diffusion, flux‐limited diffusion and fluid‐enhanced recrystallization, all operating at the scale of a single thin section and primarily controlled by host mineral microstructural setting. These findings illustrate how the development of simple partitioning coefficients (cf. garnet/zircon) and geospeedometry based on experimentally determined diffusion coefficients on grain separates may not be achievable. However, it highlights the utility of combining age and trace element concentrations from multiple accessory minerals with microstructural information when trying to build a complete history of tectonothermal events experienced by an ancient rock system that has undergone a prolonged history of thermal, deformational and fluid flow events. [ABSTRACT FROM AUTHOR]

In this paper, we study Chaplain–Lolas model in three dimensional bounded domain, which describes the invasion and diffusion process of solid tumors during the vascular growth stage. Although the model has received extensive attention since it was proposed, the existence of solutions in three-dimensional space is still missing, and only a global small solution is established by Pang and Wang (Math Models Methods Appl Sci 28(11):2211–2235, 2018) with sufficiently small proliferation coefficient. As for long time behavior, there are only corresponding stability result of constant steady-state for the case without ECM remodelling (Hillen et al. in Math Models Methods Appl Sci 25(1):165–198, 2013; Tao and Winkler in SIAM J Math Anal 47:4229–4250, 2016). If the remodeling effect of ECM is considered, the relevant research is still blank. In this paper, we first pay our attention to the study of existence of global strong solution and long time behavior. We prove that when the ratio of cell proliferation coefficient to chemotactic intensity μ χ 2 is large, there exists a unique global strong solution around the equilibrium state (1, 1, 0), and the global strong solution converges exponentially to the constant equilibrium point. In fact, such a largeness restriction on μ χ 2 is actually necessary to some extent, since that the constant equilibrium point (1, 1, 0) is actually linearly unstable when such a condition is not satisfied. Subsequently, we turn our attention to the study of dynamic behavior of solutions. We introduce a time periodic external force to this system, and prove that the solution will gradually show the same periodic behavior under the action of periodic external force, and become a time periodic solution. At last, we analysis the stability and instability of equilibrium points, and discuss the influence of spatial diffusion, chemotaxis and haptotaxis effect on the stability of solutions. In particular, we find that only chemotaxis can change the stability of the solution and make the originally stable equilibrium (1, 1, 0) unstable, while the haptotactic term has no effect on the stability. [ABSTRACT FROM AUTHOR]

The challenge of producing dense fine-grained high-entropy ceramics is hereby addressed by a combined cold and conventional pressureless sintering method for the first time. It provides nearly fully dense high-entropy pyrochlores with better microstructural homogeneity, and only half the grain size of conventional pressurelessly sintered samples with identical density. Both the finer and more homogeneous microstructures benefit better mechanical properties in hardness and reduced Young's modulus. The kinetics and activation energies of both densification and grain growth were quantified and discussed to understand how cold sintering affects the microstructural evolution during the following pressureless sintering. More importantly, cathodoluminescence analysis suggested that cold sintering could cause more defects on the surface of the original particles, which could promote the grain boundary diffusion and have drag effects on grain boundary motion. The lessons learned here offer scientific understanding and technological guidance towards pressureless sintering of dense bulk high-entropy ceramics. [ABSTRACT FROM AUTHOR]

The thermal decomposition and sintering kinetics of microfine magnesite were investigated to inaugurate a new One-step process for preparing high-density sintered magnesia. The optimal parameters for the discharging particle size of magnesite through ball milling were determined using an orthogonal experiment and Three-Way Measures ANOVA. The model for the thermal decomposition process of microfine magnesite was established through TGA-DSC and nonlinear regression analysis. Meanwhile, by describing the sintering process of microfine magnesite in detail through microstructure and CTE, the kinetic mechanisms of grain growth at different sintering stages were obtained. The results revealed that increasing the ratio of ball to powder can quickly obtain microfine magnesite which the bulk density reaches 3.45 g·cm−3 after One-step sintering. The thermal decomposition process required an activation energy of only 124.98 kJ·mol−1, which is much lower than existing technology and followed the Two-dimensional phase boundary reaction mechanism R 2. Additionally, the densification process was dominated alternatively by grain boundary diffusion and volume diffusion. This paper provided a detailed theoretical basis and leads a new direction in the One-step preparation of high-density sintered magnesia. [ABSTRACT FROM AUTHOR]

In this study, we successfully synthesized silicon nanotubes (Si-NTs) and silicon nanowires (Si-NWs) in a controllable manner using a catalyst- and template-free method through the direct electrolysis of SiO2 in a molten CaCl2-CaO system, while also proposing a novel formation mechanism for Si-NTs. Si-NWs are formed through electro-deoxidation when the cell voltage is within the range of CaO decomposition voltage and SiO2 decomposition voltage. By subsequently adjusting the voltage to a value between the decomposition potentials of CaCl2 and CaO, in-situ electro-deoxidation of CaO takes place on the surface of the synthesized Si-NWs, leading to the formation of a Ca layer. The formation of Ca-Si diffusion couple leads to the creation of vacancies within the Si-NWs, as the outward diffusion rate of Si exceeds the inward diffusion rate of Ca. These differential diffusion rates between Si and Ca in a diffusion couple exhibit an analogy to the Kirkendall effect. These vacancies gradually accumulate and merge, forming large voids, which ultimately result in the formation of hollow SiCa-NTs. Through a subsequent dealloying process, the removal of the embedded calcium leads to the formation of Si-NTs. Following the application of a carbon coating, the Si-NTs@C composite showcases a high initial discharge capacity of 3211 mAh·g−1 at 1.5 A·g−1 and exhibits exceptional long-term cycling stability, maintaining a capacity of 977 mAh·g−1 after 2000 cycles at 3.0 A·g−1. [ABSTRACT FROM AUTHOR]

All inorganic metal halide perovskite nanocrystals (NCs) have attracted much attention for their outstanding optoelectronic properties, which can be tuned by the composition, surface, size and morphology in nanoscale. Herein, we report the microfluidic synthesis of hollow CsPbBr3 perovskite NCs through the nanoscale Kirkendall effect. The formation mechanism of the hollow structure (Kirkendall void) controlled by the temperature, flow rate, ratios of precursors and ligands was investigated. Compared with the solid CsPbBr3 NCs of the same size, the hollow CsPbBr3 NCs exhibit blue shifts in ultraviolet–visible (UV–vis) absorption and photoluminescence (PL) spectra, and remarkably longer PL average lifetime (~ 98.2 ns). Quantum confinement effect, inner surface induced additional trap states and lattice strain of the hollow CsPbBr3 NCs were discussed in understanding their unique optoelectronic properties. The hollow CsPbBr3 NC based photodetector exhibits an outstanding negative photoconductivity (NPC) detectivity of 8.9 × 1012 Jones. They also show potentials in perovskite NC based photovoltaic and light emitting diodes (LEDs). [ABSTRACT FROM AUTHOR]

As a first step toward developing a downsized and high-performance O2 separator suitable for large-scale industrial applications, such as steelmaking, we have studied nanocrystalline Ag alloy thin films with high O2 permeability via rapid diffusion at Ag grain boundaries, operating at plant-waste heat temperatures (200 °C to 500 °C). In the present study, fabrication of nanocrystalline Ag–2at. pctCu–10at. pctAl alloy thin films with Ag grain size below 10 nm was attempted via reactive sputtering in Ar–O2 using grain boundary pinning force of a large number of alumina particles. Cross-sectional observation of the fabricated thin film showed that the Ag grain size ranged from 4 to 15 nm when the film thickness was less than 200 nm, but when the film thickness exceeded 200 nm, the Ag grains abruptly coarsened, reaching a maximum grain size of 214 nm. Furthermore, large surface irregularities with sizes of up to 500 to 600 nm (equivalent to 2/3 of the film thickness) were also observed. Heat transfer analysis revealed that the Ag film partially melted because of the large amount of heat released by the oxidation of Al during sputtering deposition. The conditions necessary for the fabrication of high-Al nanocrystalline Ag alloy thin films via reactive sputtering in Ar–O2 gas without film melting were clarified. [ABSTRACT FROM AUTHOR]

Introduction: Smokers frequently display respiratory symptoms despite the fact that their pulmonary function tests (PFTs) can be normal. Quantitative lung ventilation single-photon emission computed tomography (SPECT/CT) can provide a quantification of lung ventilatory homogeneity and could prove useful as an early marker of airway disease in smokers. We measured the effects of smoking on regional ventilation distribution in subjects with normal lung function and evaluated whether ventilation distribution in these subjects is related to lung function tests results and clinical symptoms. Methods: Subjects without any history of respiratory disease were prospectively recruited and separated in two groups: active smokers (AS: =10 cigarettes/day and history of =15 pack-years) and never smokers (NS: lifetime exposure of <5 cigarettes). All subjects performed PFTs (which had to be normal, defined as zscore values of forced expiratory volume in 1 s (FEV1), forced vital capacity (FVC), FEV1/FVC ratio, total lung capacity (TLC) residual volume and diffusion capacity (DLCO) all falling between -1.65 and +1.65) and underwent SPECT/CT with Technegas, which generated subject-specific ventilation heterogeneity maps. The area under the compensated coefficient of variation (CV) density curve for CV values > 40%, (AUC-CV40%) was used as the measure of ventilation heterogeneity. Results: 30 subjects were recruited (15 per group). Subjects in the AS group displayed higher dyspnea levels (1 [1-2] vs. 0 [0-1] units on mMRC scale, p < 0.001). AUC-CV40% was significantly higher in the AS group (0.386 ± 0.106 vs. 0.293 ± 0.069, p = 0.004). AUC-CV40% was significantly correlated to FEV1 (rho = -0.47, p = 0.009), DLCO (rho = -0.49, p = 0.006), CAT score (rho = 0.55, p = 0.002) and mMRC score (rho = 0.54, p = 0.002). Subjects with mMRC >0 had higher AUC-CV40% values than those without dyspnea (0.289 ± 0.071 vs. 0.378 ± 0.102, p = 0.006), while FEV1 and DLCO were not different between those groups. ROC analyses showed that the AUC for AUC-CV40% in identifying subjects with mMRC score >0 was 0.78 (95%CI 0.61-0.95, p = 0.009), which was significantly higher than that of FEV1 and DLCO. Discussion: In smokers with normal lung function, ventilatory inhomogeneities can be quantified using SPECT/CT. AUC-CV40% values are related to lung function decline and to respiratory symptomatology, suggesting a potential role for this marker in the evaluation of symptomatic smokers. [ABSTRACT FROM AUTHOR]

Parahydrogen‐induced polarization (PHIP) is an inexpensive way to produce hyperpolarized molecules with polarization levels of >10 % in the solution‐state, but is strongly limited in generality since it requires chemical reactions/ interactions with H2. Here we report a new method to widen the scope of PHIP hyperpolarization: a source molecule is produced via PHIP with high 13C polarization, and precipitated out of solution together with a target species. Spin diffusion within the solid carries the polarization onto 13C spins of the target, which can then be dissolved for solution‐state applications. We name this method PHIP‐SSD (PHIP with solid‐state spin diffusion) and demonstrate it using PHIP‐polarized [1‐13C]‐fumarate as the source molecule, to polarize different 13C‐labelled target molecules. 13C polarizations of between 0.01 and 3 % were measured on [1‐13C]‐benzoic acid, depending on the molar ratio of fumarate:benzoate in the solid state. We also show that PHIP‐SSD does not require specific co‐crystallization conditions by grinding dry powders of target molecules together with solid fumarate crystals, and obtain 13C signal enhancements of between 100 and 200 on [13C,15N2]‐urea, [1‐13C]‐pyruvate, and [1‐13C]‐benzoic acid. This approach appears to be a promising new strategy for facile hyperpolarization based on PHIP. [ABSTRACT FROM AUTHOR]

Dissolution of calcite in water is fundamental to geochemistry. Laboratory methods generally give consistent dissolution rates under conditions far from equilibrium, but close to equilibrium the measurement of dissolution using isotopes is complicated by poorly understood calcite-fluid isotopic exchange processes. This near-equilibrium isotopic exchange occurs in laboratory experiments at rates of order 10-9 to 10-13 mol/m2/s and decreases with experiment duration approximately as 1/time where time is measured from the start of the experiment. Such rates are fast enough to compete with dissolution in days-long experiments and consequently, net dissolution rates may not be measurable with isotopic tracer methods except in experiments carried out for long enough to allow the background exchange to dissipate sufficiently. To better define what should be expected for isotopic signals during dissolution, we develop a quasi-1D model for calcite dissolution that includes the mechanistically unconstrained isotopic exchange as well as solid state diffusion. We use the model, the observations reported in the literature, and the calcite dissolution rates in seawater reported by Naviaux et al., (2019a) to illustrate ambiguities in measurement of near-equilibrium calcite dissolution rates. The results suggest that the reaction order of calcite dissolution close to equilibrium could be 2 at both room temperature and the lower temperatures of the seafloor. The reaction order of near-equilibrium calcite dissolution is important for understanding calcite mineral surface processes, long-term behavior of dissolution on the seafloor, and alkalinity fluxes from modern seafloor sediments. Distinguishing between net dissolution, which affects fluid saturation state, and "exchange," which doesn't, is important but typically cannot be done with isotopic tracers alone. [ABSTRACT FROM AUTHOR]

Mullite bond coats filled with silicon particles have recently been proposed for the next generation of environmental barrier coatings (EBC). The sacrificial oxidation of the silicon particles eliminates some of the environmental durability issues associated with traditional EBC designs. To investigate this novel design approach, a mathematical formulation and resulting numerical method have been developed for simulating the oxidation of silicon particles embedded in a mullite matrix. The focus is on the oxidation of the silicon in a dry oxygen environment where the oxidant is presumably oxygen. Oxygen transport from the exterior environment through the mullite is assumed to occur via two lattice defect diffusion mechanisms. As a result, the rate of oxygen transport is dictated by the self-diffusivity of the lattice defects. The numerical method is implemented using the COMSOL Multiphysics® Program. The method is applied to simulate the oxidation of silicon particles in a mullite pellet in recent oxidation experiments. Numerical results compare favorably with the oxidation behavior observed in the oxidation experiments. The numerical method is also used to investigate the effects of various features of the mullite/silicon particle system on the oxidation behavior. [ABSTRACT FROM AUTHOR]

Reversible protonic ceramic electrochemical cells (R‐PCECs) have garnered significant attention owing to their proficiency in efficiently converting and storing energy. The performance of R‐PCECs is largely limited by the activity and durability of oxygen reduction/evolution reactions in air electrodes. Herein, an Nb and Y doped cobalt‐based double perovskite of PrBaCo1.8Nb0.1Y0.1O5+δ (denoted as PBCNY) is reported. The perovskite is however in situ assembled into a deficient‐PrBa1−xCo1.8Nb0.1−xY0.1−xO5+δ parental phase and a Ba2YNbO6 secondary phase during operation, accordingly demonstrating a low area‐specific resistance of 0.24 Ω cm2 at 600 °C. The high activity is attributed to the enhancement in oxygen vacancy concentration, oxygen surface exchange, and bulk diffusion coefficient, confirmed by X‐ray photoelectron spectroscopy and electrical conductivity relaxation. At 700 °C, when the PBCNY cathode is applied as air electrodes for R‐PCECs, a peak power density of 1.99 W cm−2 and a current density of −5.20 A cm−2 (at 1.3 V) are achieved in fuel cell (FC) mode, and electrolysis (EL) mode with appropriate Faradaic efficiencies. Furthermore, R‐PCECs with PBCNY air electrodes display promising operational stability in FC mode (over 100 h), EL mode (over 200 h), and reversible cyclic testing (29 cycles for 120 h). [ABSTRACT FROM AUTHOR]

The rate performance, power density, and energy efficiency of electrochemical devices are often limited by ionic conductivities in electrolyte and electrode materials. Framework Prussian blue analogs and dense niobium oxides have been identified as high‐rate electrodes for sodium‐ and lithium‐ion batteries, respectively, yet the origin of the extremely high solid‐state Na+/Li+ transport is not fully understood. Of critical importance is the fact that their ultra‐low activation energy and anomalous pre‐exponent factor cannot be satisfactorily rationalized from conventional theory of solid‐state diffusion in the crystal lattice. Here, assisted by density‐functional‐theory calculations, we argued that the true origin is a unique surface‐like diffusion mechanism of the intercalation ions. In a surface‐like migration event, a mobile ion moves along the channel wall via a low coordination number and low migration barrier experiencing minimal steric hindrance. It is similar to surface diffusion in the conventional picture and contrasts with lattice diffusion from one interstitial/vacancy site to another one with high coordination number, crowded saddle‐point geometry and high migration barrier. We found that the shifting from solid‐state lattice diffusion to surface‐like diffusion is determined by the size difference between the mobile ion and the diffusion channel, and a lowest migration energy barrier can be reached by mediating the channel size. The analogy to gas diffusion in molecular sieves shall be discussed. Additionally, the effects of defects and crystal water in Prussian blue analogs were also discussed for better understanding their rate performances in experimental scenarios. [ABSTRACT FROM AUTHOR]

In this investigation, calcined Ni/Mo hydrotalcite was prepared via co-precipitation method and used as a sorbent for efficient removal of lead from aqueous solutions. The Pb2+ removal efficiency reached 99% at pH 6 and a sorbent dose of 2 g/L. The equilibrium data were satisfactorily fitted by the Langmuir and Hill models with a maximum capacity of 196.87 mg/g, indicating the monolayer sorption for lead over calcined Ni/Mo hydrotalcite. The Pb2+ sorption kinetic follows a pseudo-second-order reaction due to high correlation coefficients (R2 > 0.99), while the Boyd's plots confirm the external mass transfer as the rate-limiting step in the Pb2+ sorption. The temperature effect indicated a spontaneous and exothermic Pb2+ uptake. Mechanisms involved in the removal process include surface precipitation, diffusion into the solid pores and isomorphic substitution with Ni2+ of the sheets. The results showed excellent selectivity for Pb2+ removal from multi-divalent cation solutions and good reusability of the sorbent for up to 10 consecutive sorption–regeneration cycles without significant loss of the removal efficiency. As an application, the treatment of wastewater containing Pb2+, generated from the battery industry has been undertaken. The Pb2+ concentration was reduced from 5.7 to 0.6 mg/L, corresponding to an abatement of 89.5%. Therefore, the sorption using calcined Ni/Mo hydrotalcite is an efficient and suitable method for the elimination of Pb2+. [ABSTRACT FROM AUTHOR]

The effect of annealing on the mechanical properties, intergranular corrosion (IGC) properties, and microstructure of Al–Mg–Zn alloys is studied. The results show that with the increase of annealing temperature, the strength of the alloy decreases, the elongation increases, and the corrosion resistance firstly increases and then decreases. The alloy exhibits a high corrosion resistance and good mechanical properties when the annealing treatment is 270 °C for 2 h. Meanwhile, the IGC mass loss value is less than 15 mg cm−2. In addition, the ultimate tensile strength, yield strength, and elongation are 416, 250 MPa, and 16.0%, respectively. The T‐Mg32(Al, Zn)49 phases are directly precipitated when annealing at 270 °C for 2 h. After sensitization, T phase gradually grows and coarsens. When the alloy is annealing at 400 °C for 2 h, a part of T phase gradually dissolves in the Al matrix. After sensitization, the Mg atoms with higher supersaturation gradually diffuse to grain boundary by bulk diffusion due to the low dislocation density and form a thin precipitate film, which deteriorates the corrosion resistance of the alloy. The details of corrosion mechanism analysis are as follows. [ABSTRACT FROM AUTHOR]

Pure boron carbide (B4C) ceramics are sintered by hot oscillating pressing at temperatures of 1700–1900 °C for different soaking times. The densification mechanism, grain growth kinetics, and mechanical properties obtained under these sintering conditions are systematically investigated. It is found that the fully densified B4C ceramic is obtained at 1900 °C within 120 min, possessing an excellent combination of hardness (≈38.5 GPa) and fracture toughness (4.8 MPa m1/2). The densification mechanisms during sintering are as follows: viscous flow at the initial stage (relative density D ranged from 55% to 65%) under 1700 °C; lattice diffusion/grain boundary diffusion at the sintering stage (62% < D$\textrm{ } D$ < 75%) of 1800 and 1850 °C; grain boundary sliding by dislocation motion at the late stage (65% < D$\textrm{ } D$ < 82%) of 1700 °C and the sintering stage (75% < D < 90%) at 1800–1900 °C; and dislocation gliding and stacking faults at the final stage (90% < D < 95%) occurring at 1850–1900 °C. The dislocation motion exhibits a critical impact on the densification process of the hot oscillating–pressed B4C ceramic. The grain growth kinetics at 1900 °C is controlled by grain boundary diffusion. [ABSTRACT FROM AUTHOR]

Pure metal nanowires (NWs) are one-dimensional nanomaterials with distinctive properties for various applications. Nevertheless, mass-growth forests have not been developed because of vapor pressure limitations, chemical reduction problems, or both. We succeeded in the mass growth of aluminum (Al) NW forests at desired locations by controlling atomic diffusion within the solid film. Whereas prior attention has focused only on how to increase the driving force, we show that focused ion beam irradiation created localized regions of high stress, which provided pathways for atomic diffusion as well as nuclei and driving forces for vertical NW growth. The underlying growth process could in principle be extended to other metals. [ABSTRACT FROM AUTHOR]

Lithium phosphorous oxynitride (LiPON) as one of the most successful solid‐state electrolytes (SSEs), has attracted great interest both in academia and technology due to its exceptional interfacial compatibility, broad electrochemical stability window, and excellent thermal stability, which enables the realization of extremely stable electrolyte/electrode interphase toward high‐energy density solid‐state lithium‐metal batteries (SSLMBs). However, insufficiency in ionic diffusion, mechanical robustness, and interfacial stability hinder its commercialization process. Herein, the characteristics of amorphous structure LiPON, fundamental understanding on the bulk ionic diffusion and electrode/electrolyte interface are systematically discussed, and the improvement strategies to boost the electrochemical performance are highlighted. Then, innovative characterization and computational methods help to unravel the design principle of LiPON are summarized. Furthermore, the approaches to realize high‐efficient preparation of LiPON are analyzed, followed by the investigation of present application of LiPON in current batteries. Finally, remaining challenges associated with the fundamental understanding and rational prediction of structure and interface design, high efficient preparation, and potential opportunities for future application of LiPON are properly prospected. [ABSTRACT FROM AUTHOR]

Glassy solids evolve towards lower-energy structural states by physical aging. This can be characterized by structural relaxation times, the assessment of which is essential for understanding the glass' time-dependent property changes. Conducted over short times, a continuous increase of relaxation times with time is seen, suggesting a time-dependent dissipative transport mechanism. By focusing on micro-structural rearrangements at the atomic-scale, we demonstrate the emergence of sub-diffusive anomalous transport and therefore temporal fractional diffusion in a metallic glass, which we track via coherent x-ray scattering conducted over more than 300,000 s. At the longest probed decorrelation times, a transition from classical stretched exponential to a power-law behavior occurs, which in concert with atomistic simulations reveals collective and intermittent atomic motion. Our observations give a physical basis for classical stretched exponential relaxation behavior, uncover a new power-law governed collective transport regime for metallic glasses at long and practically relevant time-scales, and demonstrate a rich and highly non-monotonous aging response in a glassy solid, thereby challenging the common framework of homogeneous aging and atomic scale diffusion. In metallic glasses, atomic-scale transport strongly affects the materials properties and thus performance in applications. Here the authors present the intermittent character of structural relaxation connected to microstructural heterogeneity, and power-law behavior at long time scales resulting from collective and correlated atomic motion. [ABSTRACT FROM AUTHOR]

Improving the oxygen diffusion capacity of solid electrolyte material is an important goal of researchers in recent decades. For this purpose, the blackening of zirconia was considered as a new strategy to enhance its oxygen diffusion capacity. We comparatively investigated the oxygen transport properties of white (YSZ, yttria stabilized zirconia) and black (ZSZ, Zr3+ stabilized zirconia) zirconia by molecular dynamics simulation. The simulation results show that the ZSZ has the same oxygen diffusion mechanism as YSZ. Furthermore, the ZSZ has a much better oxygen diffusion capacity than YSZ, which is confirmed by the lower minimum oxygen diffusion activation energy of ZSZ (0.37 eV) than that of YSZ (0.46 eV). The different oxygen diffusion capacity between YSZ and ZSZ is attributed to their crystal structure difference. The Zr3+ ionic radius is much closer to that of Zr4+ than that of Y3+, and it induces smaller lattice distortion in stabilized zirconia to impose a minimal steric blocking effect on the oxygen diffusion process. Therefore, the Zr3+ is preferred over Y3+to enhance the oxygen diffusion capacity of stabilized zirconia and the black YSZ co-doped by Y3+ and Zr3+ is proven to be a promising solid electrolyte material with a better oxygen diffusion capacity than YSZ. [ABSTRACT FROM AUTHOR]

The creep properties of fully lamellar γ/α2 titanium aluminides can be significantly improved by alloying with Nb, Ta or Zr. While the influence of these alloying elements on the γ-phase has already been examined, their diffusivity and strengthening properties in the α2-phase are still lacking. In order to study the effect of Nb, Ta and Zr in α2-Ti3Al, the alloys Ti-33Al, Ti-33Al-5Nb, Ti-33Al-5Ta and Ti-33Al-5Zr were investigated using a diffusion couple approach and strain rate jump tests. The results show that Zr diffuses the fastest, followed by Nb and Ta. Furthermore, these alloying elements also increase the strength compared to a binary Ti-33Al alloy, from which Zr leads to the highest strength increase followed by Ta and Nb. The lower diffusivity of Ta becomes increasingly important at higher temperatures and lower strain rates resulting in a higher strengthening potential than Nb and Zr under such conditions. [ABSTRACT FROM AUTHOR]

The generalized thermoelastic diffusion model is introduced and applied to an isotropic cylinder. The cylinder is under the effect of thermal flux and chemical potential. Some modifications are made to the Green and Naghdi model. Creative multi-phase-lag models with and without energy dissipation are proposed to discuss the thermoelastic diffusion of the circular solid cylinders. The analytical solutions of thermoelastic diffusion governing equations of the solid cylinders have been deduced. Comparing examples are presented between the simple and refined Green–Naghdi of types II and III models. The validity of results is worthy and benchmark outcomes are accounted for to help different specialists in their future examinations. [ABSTRACT FROM AUTHOR]

The research article deals with the reflection of plane waves in a micropolar thermoelastic diffusion solid half-space with voids in the context of Lord-Shulman theory of thermoelasticity. The governing equations are formulated to obtain two velocity equations. The plane wave solution of these velocity equations indicate the existence of six plane waves, a set of four coupled longitudinal displacement waves and a set of two coupled transverse displacement wave namely coupled longitudinal displacement wave $ (LD - 1) $ (LD − 1) , coupled thermal wave $ (LD - 2) $ (LD − 2) , coupled mass diffusion wave $ (LD - 3) $ (LD − 3) , coupled longitudinal void volume fraction wave $ (LD - 4) $ (LD − 4) and coupled transverse displacement wave $ (TD - 1) $ (TD − 1) , coupled transverse micro-rotational wave $ (TD - 2) $ (TD − 2). A reflection of the plane wave from a stress-free thermally insulated surface is studied to obtain the reflection coefficients and energy ratios of reflected waves. The reflection coefficients and energy ratios of the reflected waves are computed for a particular material and the variations of the reflection coefficients and energy ratios against the angle of incidence are shown graphically. [ABSTRACT FROM AUTHOR]

Owing to their structural diversity and mesoporous construction, metal–organic frameworks (MOFs) have been used as templates to prepare mesoporous metal oxides, which show excellent performance as anode materials for lithium-ion batteries (LIBs). Co-ZnO/C and Co-Co3O4/C nanohybrids were successfully synthesized based on a precursor of Co-doped MOF-5 by accurately controlling the annealing temperature and atmosphere. Experimental data proved that their electrochemical performance was closely associated with the material phase, especially for Co-ZnO/C, indicating that carbon skeleton materials can maintain a good restoration rate of over 99% after undergoing high-current density cycling. Meanwhile, Co-Co3O4/C nanohybrids showed an exceedingly high reversible capacity of 898 mAh∙g−1 at a current density of 0.1 C after 100 cycles. Their improved coulombic efficiency and superior rate capability contribute to a mesoporous structure, which provides pathways allowing for rapid Li+ diffusion and regulates volume change during charge and discharge processes. [ABSTRACT FROM AUTHOR]

We consider a class of bulk-surface reaction-adsorption-diffusion systems, i.e. a coupled system of reaction-diffusion systems on a bounded domain Ω ⊆ R d (bulk phase) and its boundary Σ = ∂ Ω (surface phase), which are coupled via nonlinear normal flux boundary conditions. In particular, this class includes a heterogeneous catalysis model with Fickian bulk and surface diffusion and nonlinear adsorption of Langmuir type, i.e. transport from the bulk phase to the active surface, and desorption. For this model, we obtain well-posedness, positivity and global-in-time existence of solutions under some realistic structural conditions on the chemical reaction network and the sorption model. We work in appropriate Sobolev-Slobodetskii settings, where we aim for a wide range for the integrability index, including in particular values p < d. [ABSTRACT FROM AUTHOR]

Water vapour diffusion resistance of solid wood panels and laminated veneer lumber panels The material composition of wood and adhesive is influenced by numerous factors during the bonding process, which is why the water vapour diffusion resistance (WVDR) of wood‐based panels is subject to a certain degree of variation. In this work, self and industrially produced panels were tested for their WVDR in dry and humid test climates. The tests show that the results are highly dependent on the corresponding adhesive system, the adhesive quantity and the board thickness. Additional evaluations of the adhesive joint formation using a microscope show a correlation between the WVDR and the thickness of the pure adhesive film. A comparison of the measured values with the information in the data sheets reveals a considerable difference. It can be concluded from this that in future the normative regulation for determining the WVDR for the product declaration should not be determined using list values, but rather measured for each product in accordance with standard EN ISO 12572. [ABSTRACT FROM AUTHOR]

Diffusion of atoms and molecules is usually driven by concentration gradients, with the influence of gravitational energy being negligible. However, for alloying components operating at exceptional rotational speeds, such as engine blades, the resulting centrifugal force significantly impacts element distribution. In hypergravity fields, the gravitational potential becomes comparable to the chemical potential, and these two factors jointly determine the diffusion process in solid solutions. This study establishes a theoretical model to quantify the influence of hypergravity on element diffusion in solids, analogous to centrifugal environments in engineering applications. Element diffusion under hypergravity, combined with different boundary conditions, is analyzed. It is found that gravitational energy in a hypergravity field promotes element diffusion when both are in the same direction. In particular, the effect of the hypergravity field on the diffusion process is determined by the difference between the density of diffusing atoms and one-third of the density of the solid substrate. This newly established model provides a valuable tool for assessing element diffusion in solids under extreme hypergravity conditions. [ABSTRACT FROM AUTHOR]

In this study, a series of biodegradable poly(butylene alkylene carboxylate‐co‐terephthalate) copolymers with varying methylene numbers in the alkylene units (0, 2, 4, and 8) are synthesized. These copolymers, namely, poly(butylene oxalate‐co‐terephthalate) (PBOT), poly(butylene succinate‐co‐terephthalate) (PBST), poly(butylene adipate‐co‐terephthalate) (PBAT), and poly(butylene sebacate‐co‐terephthalate) (PBSeT), are prepared with nearly identical structural and molar compositions. The objective of this study is to comprehensively examine the impact of alkylene unit length on the barrier properties of the materials, delving into aspects such as crystallinity, free volume, molecular chain mobility, as well as adsorption and diffusion of gases within the materials. The findings indicate a decrease in crystallinity from 17.2% for PBOT to 10.2% for PBSeT as the alkylene chain length increases, while maintaining the same chemical composition. Concurrently, the fractional free volume increases from 0.9% to 2.6%, and the melt flow activation energy decreases from 106.6 to 52.1 kJ mol−1. Importantly, theoretical calculations are performed, demonstrating that the predominant site for gas adsorption and diffusion is within the material's free volume. These combined observations indicate a gradual decrease in barrier properties as the number of methylene groups increases. [ABSTRACT FROM AUTHOR]

Notwithstanding the impressive phase stability and low thermal conductivity exhibited by lanthanum zirconate (LZ), its low coefficient of thermal expansion is deemed a paramount limitation. In the present study, (La 1-x Y x) 2 Zr 2 O 7 with x = 0, 0.1, 0.2, 0.3, 0.4, 0.5, as new TBCs, were synthesized by reverse co-precipitation and calcination method. The XRD and Raman analyses elucidated that the substitution of Y3+ ions occurred exclusively at the La3+ positions. In addition, in accordance with FESEM and DTA findings, the incorporation of Y 2 O 3 has induced a reduction in particle size and an enhancement in crystallization resistance. The evaluation of the coefficient of thermal expansion (CTE) demonstrated a notable improvement following the introduction of Y 2 O 3. Specifically, the CTE of LZ increased from 9.34 × 10−6 °C-1 to 10.5 × 10−6 °C-1 in the case of (La 0.5 Y 0.5) 2 Zr 2 O 7 at 1100oC. Investigations of phase stability following a 50 h heat treatment at 1300oC indicated that Y 2 O 3 had no impact on phase stability. All compounds, similar to LZ, exhibited excellent phase stability. Furthermore, the addition of Y 2 O 3 significantly amplified the grain boundary diffusion mechanism during heat treatment, leading to an accelerated grain growth rate. The grain growth rate increased from 1.7 nm/h at LZ to 2.2 nm/h in the case of (La 0.6 Y 0.4) 2 Zr 2 O 7. [ABSTRACT FROM AUTHOR]

The chloride diffusivity of calcium silicate hydrate (C-S-H), as the main hydration product of cement paste, plays an important role for the durability of concrete structures, especially for low w/c ratio ones. In this paper, in order to measure the chloride diffusion coefficient of C-S-H, a diffusion path conversion method is proposed to convert the primary diffusion path of ions from capillary pores to gel pores. By combining diffusion path conversion method with steady-state migration test, the diffusion coefficients of C-S-H are obtained. Based on 3D nanostructure, which is generated by a hybrid scheme of Grand Canonical Monte Carlo and Molecular Dynamics, the chloride diffusion coefficient of C-S-H is predicted by a 3D diffusive lattice modelling. Results from the experiments and simulation are compared with the data in the literature. Our work contributes to the understanding of C-S-H diffusivity and is of great importance for predicting the long-term durability of concrete structure. [ABSTRACT FROM AUTHOR]

The transition from heterogeneous nucleation of nanoscale hardening S-phase precipitates on dislocation lines in cold-rolled aluminium alloy 2024 (Al–Cu–Mg) to a spatially homogeneous distribution during artificial ageing is studied by means of in situ and ex situ transmission electron microscopy (TEM). Three stages of precipitate evolution following nucleation on dislocation lines are established: (i) Growth and coalescence on dislocation lines, (ii) Ostwald ripening controlled by pipe diffusion, and (iii) Ostwald ripening controlled by volume diffusion. Whilst Ostwald ripening controlled by pipe diffusion is active (stage (ii) and transition from stage (ii) to stage (iii)) dislocation annihilation and/or re-arrangement can occur. [ABSTRACT FROM AUTHOR]

By employing metal oxides as oxygen carriers, chemical looping demonstrates its effectiveness in transferring oxygen between reduction and oxidation environments to partially oxidize fuels into syngas and convert CO2 into CO. Generally, NiFe2O4 oxygen carriers have demonstrated remarkable efficiency in chemical looping CO2 conversion. Nevertheless, the intricate process of atomic migration and evolution within the internal structure of bimetallic oxygen carriers during continuous high‐temperature redox cycling remains unclear. Consequently, the lack of a fundamental understanding of the complex ionic migration and oxygen transfer associated with energy conversion processes hampers the design of high‐performance oxygen carriers. Thus, in this study, we employed in situ characterization techniques and theoretical calculations to investigate the ion migration behavior and structural evolution in the bulk of NiFe2O4 oxygen carriers during H2 reduction and CO2/lab air oxidation cycles. We discovered that during the H2 reduction step, lattice oxygen rapidly migrates to vacancy layers to replenish consumed active oxygen species, while Ni leaches from the material and migrates to the surface. During the CO2 splitting step, Ni migrates toward the core of the bimetallic oxygen carrier, forming Fe–Ni alloys. During the air oxidation step, Fe–Ni migrates outward, creating a hollow structure owing to the Kirkendall effect triggered by the swift transfer of lattice oxygen. The metal atom migration paths depend on the oxygen transfer rates. These discoveries highlight the significance of regulating the release–recovery rate of lattice oxygen to uphold the structures and reactivity of oxygen carriers. This work offers a comprehensive understanding of the oxidation/reduction‐driven atomic interdiffusion behavior of bimetallic oxygen carriers. [ABSTRACT FROM AUTHOR]

The development of efficient oxygen evolution reaction (OER) electrocatalysts is critical to overcome the efficiency bottleneck in hydrogen generation via water electrolysis. Hollow nanostructured materials have emerged as a hot topic for electrocatalysis research because of their advantages, including abundant active sites, a large contact area between the catalyst and the electrolyte, and a short transmission path. As highly efficient and stable OER electrocatalysts, cobalt‐based nanostructured materials have attracted more and more attention. In this work, cobalt metal/cobalt phosphides/nitrogen‐doped carbon composites (Co‐CoxP/NC) with a hierarchical hollow structure are designed by using hollow ZIF‐67 microspheres as precursors. By coating ZIF‐8 on the surface of hollow ZIF‐67 microspheres and further carbonizing, carbon nanowhiskers are successfully formed on the surface of hollow carbon spheres under the catalytic effect of Co nanoparticles at a high temperature. In the subsequent phosphating process, solid Co nanocrystalline particles are transformed into core–shell CoP and Co2P nanoparticles on account of the Kirkendall effect. Through the optimization of the microstructure of the material and the synergistic effect of transition metal, transition metal phosphide, and nitrogen doping, the overpotential of the optimal material is only 287 mV at 10 mA cm−2 current density in 1 m KOH. [ABSTRACT FROM AUTHOR]

Protonic ceramic electrolysis cells (PCECs) have attracted significant attention as a promising technology for green hydrogen production and conversion. However, traditional PCECs oxygen electrodes exhibit poor electrochemical performance because of their limited hydration ability and lack of intrinsic protonic conductivity. In this study, a W-doped perovskite oxide, Sr 2 Fe 1.5 Mo 0.4 W 0.1 O 6-δ (SFMW), with a strong hydration capacity and an accelerated proton mobility, was designed to serve as the oxygen electrode in PCECs. The results indicate that W doping enhances the concentration of oxygen vacancies in Sr 2 Fe 1.5 Mo 0.5 O 6-δ (SFM) and facilitates the adsorption of H 2 O onto the oxygen electrode, thereby significantly accelerating proton mobility. The bulk diffusion coefficient of protons (D H) in SFMW, estimated through electrical conductivity relaxation measurement, can reach up to 2.86 × 10−5 cm∙s−1 at 750 °C, which is significantly higher than that of SFM (7.96 × 10−6 cm∙s−1). Consequently, SFMW exhibited impressive electrochemical performance, as evidenced by its lower polarization resistance (0.072 Ω⋅cm2, 700 °C in air) and higher current density (945 mA/cm2 with a voltage of 1.3 V at 650 °C) in PCECs. These results suggest that accelerating bulk proton transfer by W doping is highly feasible and holds great potential for the development of oxygen electrodes for high-activity PCECs. [ABSTRACT FROM AUTHOR]

Localized high‐concentration electrolyte (LHCE) is considered to be a promising substitution for the conventional carbonate electrolytes in fast‐charging Li‐ion batteries. However, the rate‐determining steps (RDS) for fast‐charging electrodes (i.e., graphite anode) in LHCE remain unclear. Herein, a typical localized high‐concentration electrolyte consisting of lithium bis(fluorosulfonyl)imide in dimethoxyethane with 1,1,2,2‐tetrafluoroethyl‐2,2,3,3‐tetrafluoropropyl ether as a diluent is selected to investigate the RDS of lithiation process in graphite anode, including the diffusion of solvated Li+ in the electrolyte, the desolvation behavior of solvated Li+, the Li+ transfer in solid electrolyte interphase (SEI) on the graphite surface, and the Li+ diffusion in bulk graphite. The results indicated that the rate performance of graphite anode in LHCE lies in the balance between Li+ desolvation process and Li+ migration in SEI. Through the regulation of solvated Li+ structure and SEI component, excellent fast‐charging performance can be obtained in the LHCE. The present studies not only offer fresh insights in the mechanistic understanding of fast‐charging batteries, but also provide new clues to the performance improvement of graphite anodes. [ABSTRACT FROM AUTHOR]

LaB6–HfB2 composites with the different HfB2 contents (10 wt.%, 30 wt.%, 50 wt.%, 70 wt.%, and 90 wt.%) were densified by spark plasma sintering (SPS). Results showed that the densification mechanism of the composite transformed from the grain boundary diffusion into the dislocation climbing mechanism as the holding time was extended from 0 to 15 min under temperature range of 1750–1900°C. The HfB2 phase could effectively limit the grain growth of LaB6 phase, and the dynamic growth of the grain was governed by grain boundary diffusion. Both the Berkovich hardness and Vickers hardness obeyed the normal indentation size effect. LaB6–70 wt.% HfB2 composite had the highest fracture toughness of 3.98 ± .43 MPa m.5, whereas the highest current density of 18.34 A/cm2 belonged to LaB6–30 wt.% HfB2 composite. All the results demonstrated that LaB6–HfB2 composite was a promising material with the excellent structural and functional performance. [ABSTRACT FROM AUTHOR]

[Display omitted] • Interface engineering and nano-effects were employed to enhance the ORR activity. • PBSC/CPO heterostructure nanofibers were constructed by in situ self-assembly combined with electrostatic spinning. • PBSC/CPO heterostructure nanofibers facilitate the charge transfer and oxygen ion transport. • PBSC/CPO heterostructure nanofibers exhibits an impressive MPD of 1363 mW cm−2 at 750 °C. The engineering and exploration of cathode materials to achieve superior oxygen reduction catalytic activity and resistance to CO 2 are crucial for enhancing the performance of solid oxide fuel cells (SOFCs). Herein, a novel heterostructure composite nanofiber cathode comprised of PrBa 0.5 Sr 0.5 Co 2 O 5+δ and Ce 0.8 Pr 0.2 O 1.9 (PBSC-CPO-ES) was prepared for the first time through a synergistic approach involving in-situ self-assembly and electrostatic spinning techniques. PBSC-CPO-ES exhibits exceptionally high oxygen reduction catalytic activity and CO 2 resistance, which is attributed to its unique nanofiber microstructure and abundant presence of heterointerfaces, significantly accelerating the charge transfer process, surface exchange and bulk diffusion of oxygen. The introduction of CPO not only effectively reduces the thermal expansion of PBSC but also changes the characteristics of oxygen ion transport anisotropy in layered perovskite materials, forming three-dimensional oxygen ion transport pathways. At 750 °C, the single cell employing the PBSC-CPO-ES heterostructure nanofiber attains an impressive peak power density of 1363 mW cm−2. This represents a notable 60.7 % improvement in comparison to the single-phase PBSC powder. Moreover, PBSC-CPO-ES exhibits excellent CO 2 tolerance and performance recovery after CO 2 exposure. This work provides new perspectives to the design and advancement of future high-performance and high-stability SOFC cathode materials. [ABSTRACT FROM AUTHOR]

Reversible protonic ceramic electrochemical cells (R‐PCECs) are very promising as energy conversion and storage devices with high efficiency at intermediate temperatures (500–700 °C). Unfortunately, the sluggish reaction kinetics on air electrodes severely hamper the commercial application of R‐PCECs. In this work, an In‐doped PrBaCo2O5+δ air electrode is developed with a designed formula of PrBaCo1.9In0.1O5+δ, which however consists of a dominated double perovskite PrBa0.95Co1.85In0.09O5+δ and a minor cubic perovskite BaCo0.85In0.15O3‐δ phase, as suggested by the XRD refinements. The formation of nanocomposites induced by the In‐doping has markedly improved the activity of oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), due likely to the increased oxygen vacancies, enhanced the oxygen surface exchange and bulk diffusion capabilities when compared to the bare PrBaCo2O5+δ. Excellent electrochemical performances in fuel cell (FC) mode (2.25 W cm−2) and electrolysis cell (EC) mode (−4.41 A cm−2 at 1.3 V) are achieved on the single cells with such nanocomposite air electrodes at 700 °C. In addition, promising durability tests of cells in modes of FC (100 h), EC (100 h), and cycling (210 h) are demonstrated at 600 °C. This In‐doped strategy provides a novel approach to developing new air electrode materials. [ABSTRACT FROM AUTHOR]